(1) Field of the Invention
The instant invention relates to a vibration isolation mount and more particularly to a vibration isolation mount which automatically compensates for sag at elevated temperatures.
(2) Description of the Prior Art
Vibration isolation mounts have heretofore been known for isolating devices, such as motors, from their surrounding environments. More specifically, the function of a vibration isolation mount is either to prevent vibratory motion of a device from propagating into its surroundings, such as in isolating a machine from its motor, or to prevent vibratory motion of a surrounding environment from travelling to a delicate device, such as in seismic isolation, or isolation from vibrations encountered in shipping and handling.
The primary element of a vibration isolation mount is a visco-elastic body element, such as a rubber cylinder, which is effective for absorbing or dissipating vibratory energy. While rubber is known to be an effective material for absorbing vibratory energy, it is also known that the mechanical properties of rubber change as a function of temperature. More specifically, it is known that the shear modulus (elastic strength) of rubber decreases as temperature increases, and that a reduction in the shear modulus of rubber causes the rubber to become more elastic or resilient.
In this regard, a rubber isolation mount which is subjected to a compressive force at an elevated temperature tends to bulge outwardly and sag in the direction of the applied mean force. This sagging phenomenon presents a particular problem when a rubber vibration isolation mount is used to isolate a rotary electric motor in a shaft operated machine. In a shaft operated machine, a rotary electric motor is typically mounted on a cylindrical vibration isolation mount, and the drive shaft of the motor is coupled to a drive shaft of the machine. The electric motor generates heat as a product of its operation, and in an enclosed space, such as a machine housing, the heat generated by the motor causes a localized increase in temperature around the motor. The increased temperature causes the rubber isolation mount to bulge outwardly and sag under the weight of the motor. The sagging of the isolation mount decreases the vertical height of the motor drive shaft and causes it to become misaligned with the machine drive shaft. Misalignment of the drive shafts provides an additional source of vibration which can cause to the motor and to the machine itself. Current design techniques attempt to solve this shaft alignment problem with special shaft couplings which allow for movement of the motor drive shaft with respect to the machine drive shaft.